1. Field of the Invention
The present disclosure generally relates to an image forming apparatus such as a copier, facsimile, and printer, and more particularly to an image forming apparatus, which can produce images on a recording medium with a one-path system.
2. Discussion of the Background
In general, an image forming apparatus can use methods such as a switch-back system and one-path system to produce images on both faces of a recording medium such as a transfer sheet.
In case of the switch-back system, the recording medium is passed through a transfer unit and then a fixing unit to record an image on one face of the recording medium, and then the recording medium is transported to a sheet inverting route to invert faces of the recording medium. Then, the recording medium is switch-backed to the transfer unit and the fixing unit to record an image on the other face of the recording medium.
In case of the one-path system, a double-side transfer mechanism transfers images to both faces of the recording medium and then the recording medium is passed through a fixing unit. Therefore, images can be recorded on both faces of the recording medium without switch-backing the recording medium.
Accordingly, the one-path system can avoid the following aspects associated with the switch-back system; a cost increase due to providing a switch-back mechanism; a longer time for image forming due to the switch-back process; a sheet jamming which might occur by switch-backing the recording medium curled by heating of a fixing unit, as examples.
However, in the one-path system, a disturbance may occur on images when transporting a recording medium from the double-side transfer mechanism to the fixing unit.
In general, a sheet transporting unit is provided between the double-side transfer mechanism and fixing unit in an image forming apparatus employing the one-path system to transport the recording medium having unfixed images on its both faces. When such a recording medium is transported from the double-side transfer mechanism to the fixing unit in the one-path system, the recording medium may be scratched by components of the sheet transporting unit because one face of the recording medium having un-fixed toner image contacts such component. With such a scratching, the un-fixed toner image on the recording medium may be disturbed.
If a toner image is transferred only to one face of the recording medium (e.g., transfer sheet), a disturbance of an un-fixed toner image can be prevented by contacting a face of the recording medium having no toner image to the component of the sheet transporting unit. Such a configuration can be designed by modifying a design layout in an image forming apparatus.
However, if toner images are transferred to both faces of the recording medium (e.g., transfer sheet), one face of the recording medium having toner image contacts the component of the sheet transporting unit, thereby a disturbance on images may occur when transporting the recording medium from the double-side transfer mechanism to the fixing unit.
In one related art, a spur, having a plurality of projections on its peripheral circumference, is provided between a double-side transfer mechanism and a fixing unit in an image forming apparatus, wherein the double-side transfer mechanism can transfer toner images to both faces a recording medium (e.g., transfer sheet), and the spur can be rotated by a driving unit.
With such a configuration, the recording medium (e.g., transfer sheet) can be guided (i.e., transported) from the double-side transfer mechanism to the fixing unit in the image forming apparatus.
The spur can support the recording medium by projections from the underside of the recording medium. With a rotation of the spur, the recording medium can be guided (i.e., transported) from the double-side transfer mechanism to the fixing unit with being supported by the spur from the underside face of the recording medium. However, the spur has projections that stick the recording medium. Thereby, un-fixed toner images on the recording medium may be disturbed, particularly if the projections of the spur have a sharp profile.
In another related image forming apparatus, a recording medium is transported from a double-side transfer mechanism to a fixing unit by interposing a transport belt between the double-side transfer mechanism and the fixing unit, wherein the double-side transfer mechanism transfers toner images to both faces of the recording medium.
Such a transport belt can be an endless type belt, which is extended by a plurality of rollers. The transport belt receives the recording medium from an intermediate transfer belt of the double-side transfer mechanism, and guides (i.e., transports) the recording medium toward the fixing unit. Specifically, a front edge of the recording medium is guided (i.e., transported) to the fixing unit by the transport belt.
In such an image forming apparatus, the transport belt and the intermediate transfer belt of the double-side transfer mechanism can be driven with a same speed, thereby the recording medium can be guided (i.e., transported) from the intermediate transfer belt to the transport belt with a same speed, by which scratching of image on the recording medium can be suppressed when the recording medium is transported from the intermediate transfer belt to the transport belt.
With such a configuration, disturbance of un-fixed toner image on the recording medium can be suppressed.
However, even in such an image forming apparatus, a counteraction may occur between the intermediate transfer belt and the transport belt when the recording medium is received by the transport belt from the intermediate transfer belt.
Although the intermediate transfer belt and transport belt can be driven at a same speed, the intermediate transfer belt and transport belt have a gap therebetween, and thereby the recording medium may receive some counteraction force when the transport belt receives the recording medium from the intermediate transfer belt.
With such counteraction force at the gap, the recording medium may be scratched by the transport belt, thereby disturbance may occur on un-fixed toner images on the recording medium.
In case of an image forming apparatus for printing a color image with higher speed on both faces of the recording medium, such disturbance of un-fixed toner images on the recording medium may occur to a greater degree.
In such an image forming apparatus for printing color image with higher speed, two tandem configurations are provided for a double-side transfer mechanism to produce an image on both faces of a recording medium. Specifically, one tandem configuration includes a first intermediate transfer belt and a first group of photosensitive members (e.g., four photosensitive members) to form toner images on the first intermediate transfer belt and then on one face of the recording medium. The other tandem configuration includes a second intermediate transfer belt and a second group of photosensitive members (e.g., four photosensitive members) to form toner images on the second intermediate transfer belt and then on another face of the recording medium.
Four photosensitive members in each of the first and second group of photosensitive members are used to form yellow (Y), magenta (M), cyan (C), and black (K) toner images. Such four photosensitive members serving as image carrying members are arranged in a parallel manner (i.e., tandem manner). Such a configuration can be used to produce a toner image on each face of the recording medium.
The Y, M, C, and K toner image formed on the photosensitive members of the first group are super-imposingly transferred to the first intermediate transfer belt, and then transferred to one face of the recording medium to produce a full-color toner image on one face of the recording medium. Similarly, the Y, M, C, and K toner image formed on the photosensitive members of the second group are super-imposingly transferred to the second intermediate transfer belt, and then transferred to the other face of the recording medium to produce a full-color toner image on the other face of the recording medium.
In such an image forming apparatus used for printing color image with higher speed, a full-color toner image can be transferred to both faces the recording medium while transporting the recording medium with higher speed.
However, because of such higher speed for transporting the recording medium, the recording medium may receive a relatively greater counteraction when the recording medium is transported from the intermediate transfer belt to the transport belt.
With such counteraction, the recording medium may be scratched by the transport belt, or sheet jamming may occur between the intermediate transfer belt and the transport belt.